Study of charm production in Z decays

The production rates of D(*+/-) D(s)(*+/-), D(+/-), D(0)/(D) over bar(0), D(s)(+/-), and Lambda(c)(+)/<(Lambda)over bar>(-)(c) in Z --> c (c) over bar decays are measured using the LEP I data sample recorded by the ALEPH detector. The fractional energy spectrum of the D(*+/-) is well described as the sum of three contributions: charm hadronisation, b hadron decays and gluon splitting into a pair of heavy quarks. The probability for a c quark to hadronise into a D(*+) is found to be f(c --> D(*+)) = 0.233 +/- 0.010(stat.) +/- 0.011(syst.). The average fraction of the beam energy carried by D(*+/-) mesons in Z --> c (c) over bar events is measured to be (X(E)(D(*+/-)))(c (c) over bar) = 0.4878 +/- 0.0046(stat.) +/- 0.0061(syst.). The D(*+/-) energy and the hemisphere mass imbalance distributions are simultaneously used to measure the fraction of hadronic Z decays in which a gluon splits to a c (c) over bar pair: (n) over bar(g --> c (c) over bar) = (3.23 +/- 0.48(stat.) +/- 0.53(syst.))%. The ratio of the Vector/(Vector+Pseudoscalar) production rates in charmed mesons is found to be P(V) = 0.595 +/- 0.045. The fractional decay width of the Z into cc pairs is determined from the sum of the production rates for various weakly decaying charmed states to be R(c) = 0.1738 +/- 0.0047(stat.) +/- 0.0116(syst.).